In my U.S. Pat. No. 5,610,907 issued Mar. 11, 1997, I disclose a wireless RF time hopping code-division-multiple-access (CDMA) and time-division-multiple-access (TDMA) spread spectrum communications systems, and specifically to ultrafast systems, which use individual ultrashort pulses (monocycle) or small number of cycles (packets) signals in the picosecond (10.sup.-12) through nanosecond (10.sup.-9) to microsecond (10.sup.-6) range. Before transmission and after reception, the system functions as a digital communications system. The carrier for such wireless communications systems is neither a frequency, amplitude, phase nor polarization carrier, but is due to the precise timing arrangements in a sequence of individual pulses provided by the digital coding schemes.
Whereas most wireless RF communications systems in the art use frequency-domain receiver designs based on the heterodyne, or super heterodyne principle, the receiver of the present invention is a time-domain homodyne receiver. Whereas prior art uses coding, e.g., in direct sequencing or frequency hopping, to achieve spreading and despreading of the signal with resultant processor gain, the present invention uses an ultrashort pulse or packet as an individual signal, as well as coding which determines the timing of such individual pulses within a sequence. Information is carried in a transmission by the pulse position modulation technique, i.e., by precise micro-deviation from the pulse sequence timing set by the channel code.
Due to the use of orthogonal coding schemes and the use of ultrafast pulse sequence techniques, it is possible to provide extremely high data rate wireless point-to-point communications, as well as wide area multimedia communications.
The invention in my above-identified patent significantly increases the data rate of wireless RF communications by using orthogonal coding schemes in ultrafast time hopping CDMA communications both in point-to-point and broadcast mode; it provides a communications system which can coexist without interfering with, or causing interference to conventional RF transmissions or other ultrafast time hopping CDMA or TDMA users; it also provides wireless communications system which can interface with digital, e.g., optical fiber, communications systems; and a communications system which is robust against environmental notched filtering of frequency components in the transmitted signal; and provides communications system which has substantial range at modest power, is small in size, weight and is not costly to manufacture.
Briefly, the above features are achieved in an RF ultrafast time hopping CDMA and TDMA wireless communications system, which uses individual pulses and packets in a sequence of such pulses or packets, those individual pulses/packets being so short in duration (e.g., in the picosecond and nanosecond range) that the individual pulse signal energy is spread over very many frequencies simultaneously or instantaneously (instead of sequentially) with respect to a slow sampling system. A time hopping sequential code is also used to position these pulses/packets precisely in sequence providing optimum use of time-frequency space and also providing noninterfering transmission channels due to the orthogonality of the coding schemes used. The ultrashort nature of the individual pulses/packets used also permits the time duration of a frame to be divided into very many microintervals of time in which the signal could occur. This division into very many microintervals in a frame permits the availability of many possible coding schemes as well as many noninterfering transmission channels. Thus the ultrashort nature of the individual pulses, together with orthogonal coding schemes, permits the highest multichannel or aggregate data rates of any wireless communications system.
In one embodiment of the invention in my above patent, a communications system uses: (i) orthogonal codes which can be slaved to a single acquisition system/matched filter and which captures and assigns each code to unique decoding modems; (ii) correlators/acquisition systems/matched filters which are able to detect the ultrafast signals and retain memory of such capture over superframes of the order of a millisecond; (iii) pulsed power sources, antennas, encoding modems, oscillator-clocks, intelligence/data encrypters; and (iv) EPROMs to provide coding information to both encoding and decoding modems.
The present invention addresses optical time hopping code-division-multiple-access (CDMA) and time-division-multiple access (TDMA) spread spectrum communications systems, and specifically ultrafast systems and high data rate systems, which use individual ultrashort signals in the femtosecond (10.sup.-15) range, but could apply to signals of other temporal lengths. Before transmission and after reception, the system functions as a digital communications system. As in my above-identified patent, the carrier for such wireless communications systems is neither a frequency, amplitude, phrase nor polarization carrier, but is due to the precise timing arrangements in a sequence of individual pulses or wave packets provided by the digital coding schemes, i.e., a macrocode.
The present invention addresses a system and method, as in my above-identified patent, in which information is transmitted by a pulse or packet position modulation technique, i.e., by precise micro-deviation from the pulse/packet sequence timing set by the channel code or microcode, e.g., by pulse/packet modulation.
Due to the use of orthogonal coding schemes and the use of ultrafast pulse sequence techniques, it is possible to provide extremely high data rate optical fiber broadcast as well as point-to-point communications.